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Managing the MAC Address Table
For more information about private VLANs, see
MAC Addresses and Switch Stacks
The MAC address tables on all stack members are synchronized. At any given time, each stack member
has the same copy of the address tables for each VLAN. When an address ages out, the address is
removed from the address tables on all stack members. When a switch joins a switch stack, that switch
receives the addresses for each VLAN learned on the other stack members. When a stack member leaves
the switch stack, the remaining stack members age out or remove all addresses learned by the former
stack member.
Default MAC Address Table Configuration
Table 7-3
Table 7-3
Feature
Aging time
Dynamic addresses
Static addresses
Changing the Address Aging Time
Dynamic addresses are source MAC addresses that the switch learns and then ages when they are not in
use. You can change the aging time setting for all VLANs or for a specified VLAN.
Setting too short an aging time can cause addresses to be prematurely removed from the table. Then
when the switch receives a packet for an unknown destination, it floods the packet to all ports in the same
VLAN as the receiving port. This unnecessary flooding can impact performance. Setting too long an
aging time can cause the address table to be filled with unused addresses, which prevents new addresses
from being learned. Flooding results, which can impact switch performance.
Beginning in privileged EXEC mode, follow these steps to configure the dynamic address table aging
time:
Command
Step 1
configure terminal
Step 2
mac address-table aging-time [0 |
10-1000000] [vlan vlan-id]
Step 3
end
Catalyst 3750 Switch Software Configuration Guide
7-22
shows the default MAC address table configuration.
Default MAC Address Table Configuration
Default Setting
300 seconds
Automatically learned
None configured
Purpose
Enter global configuration mode.
Set the length of time that a dynamic entry remains in the MAC
address table after the entry is used or updated.
The range is 10 to 1000000 seconds. The default is 300. You can also
enter 0, which disables aging. Static address entries are never aged
or removed from the table.
For vlan-id, valid IDs are 1 to 4094. Do not enter leading zeros.
Return to privileged EXEC mode.
Chapter 7
Chapter 15, "Configuring Private VLANs."
Administering the Switch
78-16180-02
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